1. Field of the Invention
The present invention relates to a polishing method for a semiconductor wafer for polishing the semiconductor wafer.
2. Description of Related Art
As a method for polishing a semiconductor wafer using a polishing slurry, there has been conventionally employed a method including a primary polishing step, a secondary polishing step and a finish polishing step. In such polishing method, the polishing slurry is reused in the primary polishing step and the secondary polishing step in terms of production cost.
As an arrangement applicable to such rough polishing steps prior to the finish polishing, there has been known a polishing system for polishing the semiconductor wafer using a recycled polishing slurry (see, for instance, Document: JP-A-2000-237959, left column of page 4 to right column of page 5).
In a system disclosed in the Document, new slurry is fed from an unused slurry feeding unit to a buffer tank, while a recycled slurry after filtering is fed from a recycle unit to the buffer tank. Then, the polishing slurries stored in the buffer tank are fed to each of polishing sections by pumps connected to each of the polishing sections, the pumps being separately controllable.
On the other hand, in the finish polishing, the polishing slurry recycled using the system disclosed in the Document is not typically used. Instead, a finishing-slurry prepared solution is used, the finishing-slurry prepared solution being prepared by adding alkaline solution and water-soluble polymer agent to silica particle to obtain a finishing-slurry stock solution and further adding purified water to the finishing-slurry stock solution.
However, when the system disclosed in the Document is applied to the rough polishing step, contaminants that are contained in the recycled polishing slurry and cannot be removed by filtering might cause a lot of minute projecting defects to be generated on the semiconductor wafer.
In addition, when the finishing-slurry prepared solution as described above is used in the finish polishing step, contaminants contained in the finishing-slurry prepared solution might cause a lot of projecting defects to be generated on the semiconductor wafer.